1. Technical Field
This disclosure generally relates to biomass torrefaction systems and methods, including in particular cellulosic biomass torrefaction systems and methods.
2. Description of the Related Art
Torrefaction of biomass particles is well known and is a process in which biomass particles are heated in a low oxygen environment. This causes volatile compounds within the particles to be boiled off and the cellular structure of the particles to be degraded, resulting in a partial loss of mass and an increase in friability. It also causes a reaction within the remaining cellular structure that enhances the moisture resistance of the product. Torrefied particles have an enhanced energy value when measured in terms of heat energy per unit of weight. The degree of torrefaction of biomass particles depends on several factors, including the level of heat applied, the length of time the heat is applied, and surrounding gas conditions (particularly with respect to oxygen level).
Current systems strive to mechanically control the variables of heat, residence time and oxygen levels to achieve consistent torrefied particles. Typical mechanisms intended to torrefy biomass particles under low level oxygen conditions use mechanical means to convey the particles (such as rotating trays or screws) and apply heat to the conveying surfaces for conduction to the particles to be torrefied. Such mechanisms suffer from a variety of drawbacks, including being difficult or impossible to significantly scale up in capacity. As the demand for torrefied biomass increases, the limited capacity of current mechanisms has become an issue impeding the use of such biomass. Consequently, Applicant believes improved methods and systems able to consistently and efficiently produce torrefied biomass particles are desirable. These methods and systems should be based on principles and concepts that allow tight process control while achieving large capacities, to meet growing demand.